In the extrusion of polymeric melts, the extrudate is usually forced through a strainer to remove particles of gel and other impurities. After a period of operation, a screen pack in the strainer becomes clogged and must be changed. Although different types are available, a particularly useful changer of the cartridge type has been disclosed by Heston in U.S. Pat. No. 3,675,934.
With reactive polymer systems, abnormal amounts of gel and/or degraded polymer can be formed on startup. As a consequence, the screen pack in the transfer line to a die clogs rapidly and must be changed so frequently as to be impractical.